Physics Nobel honors underpinnings of exotic matter

 nobelprize2016 phyImage credit: Nobelprize.org

A trio of researchers who laid the foundation for understanding numerous exotic phases of matter have split the 2016 Nobel Prize in Physics.

The Royal Swedish Academy of Sciences awarded the prize "for theoretical discoveries of topological phase transitions and topological phases of matter" to three laureates: David Thouless of the University of Washington, Duncan Haldane of Princeton University and Michael Kosterlitz of Brown University.

The research behind the prize "illustrates, in a very nice way, the interplay between physics and mathematics," said Thors Hans Hansson, a physicist who introduced the mathematics behind the prize at the announcement ceremony using a cinnamon bun, a bagel and a pretzel.

Topology is the branch of mathematics that offers a coarse distinction between those three baked goods, often capturing differences by counting the number of holes that different objects have. In topology, a bagel and a pretzel are fundamentally different because there is no way to add more holes to a bagel without tearing the dough and reshaping it.

The application of topology to physics was a revelation in the late 1970s and 1980s. Many puzzling behaviors defied explanation until topology was considered. For example, experiments on thin materials subjected to low temperatures and enormous magnetic fields exhibited an odd behavior. Instead of their electrical current changing continuously as a magnetic field varied, it made discrete jumps. Now known as the quantum Hall effect, this behavior arose from the topological properties of electrons in the material. When confined to two dimensions and subjected to extreme conditions, the quantum behavior of electrons can get knotted up in topologically distinct ways. This realization explained where the jumps in current occurred and why they were stable even when samples were less than pristine.

Many researchers at JQI, CMTC and CNAM take advantage of the interplay between topology and physics, using it to guide light in novel ways or study how to build a quantum computer. They've even extended some of the early work by Thouless to create a quantum pump.

Stay tuned for updates as we continue to follow this year's Nobel Prize in Physics.  Please visit JQI to follow the updates.

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UMD Physicists Discover “Smoke Rings” Made of Laser Light

3D ring structures made by high-intensity lasers could aid the design of powerful microscopes and more efficient telecommunication lines

Most basic physics textbooks describe laser light in fairly simple terms: a beam travels directly from one point to another and, unless it strikes a mirror or other reflective surface, will continue traveling along an arrow-straight path, gradually expanding in size due to the wave nature of light. But these basic rules go out the window with high-intensity laser light. ­­­

Powerful laser beams, given the right conditions, will act as their own lenses and "self-focus" into a tighter, even more intense beam. University of Maryland physicists have discovered that these self-focused laser pulses also generate violent swirls of optical energy that strongly resemble smoke rings. In these donut-shaped light structures, known as "spatiotemporal optical vortices," the light energy flows through the inside of the ring and then loops back around the outside.

The vortices travel along with the laser pulse at the speed of light and control the energy flow around it. The newly discovered optical structures are described in the September 9, 2016 issue of the journal Physical Review X.

The researchers named the laser smoke rings "spatiotemporal optical vortices," or STOVs. The light structures are ubiquitous and easily created with any powerful laser, given the right conditions. The team strongly suspects that STOVs could explain decades' worth of anomalous results and unexplained effects in the field of high-intensity laser research.

"Lasers have been researched for decades, but it turns out that STOVs were under our noses the whole time," said Howard Milchberg, professor of physics and electrical and computer engineering at UMD and senior author of the research paper, who also has an appointment at the UMD Institute for Research in Electronics and Applied Physics (IREAP). "This is a robust, spontaneous feature that's always there. This phenomenon underlies so much that's been done in our field for the past 30-some years."

Milchberg inline image Orbital angular momentum (OAM) vortices (pink ringlike objects) are three-dimensional laser light structures that rotate around a central beam, much like water circles around a drain. Physicists and engineers have studied this type of laser vortex since the 1990s as a tool to help improve microscopy and telecommunications. Image credit: Howard Milchberg

More conventional spatial optical vortices are well-known from prior research—chief among them "orbital angular momentum" (OAM) vortices, where light energy circulates around the beam propagation direction much like water rotates around a drain as it empties from a washbasin. Because these vortices can influence the shape of the central beam, they have proven useful for advanced applications such as high-resolution microscopy.

"Conventional optical vortices have been studied since the late 1990s as a way to improve telecommunications, microscopy and other applications. These vortices allow you to control what gets illuminated and what doesn't, by creating small structures in the light itself," said the paper's lead author Nihal Jhajj, a physics graduate student who conducted the research at IREAP.

"The smoke ring vortices we discovered may have even broader applications than previously known optical vortices, because they are time dynamic, meaning that they move along with the beam instead of remaining stationary," Jhajj added. "This means that the rings may be useful for manipulating particles moving near the speed of light."

Jhajj and Milchberg acknowledge that much more work needs to be done to understand STOVs, including their physical and theoretical implications. But they are particularly excited for new opportunities that will arise in basic laser research following their discovery of STOVs.

"All the evidence we've seen suggests that STOVs are universal," Jhajj said. "Now that we know what to look for, we think that looking at a high-intensity laser pulse propagating through a medium and not seeing STOVs would be a lot like looking at a river and not seeing eddies and currents."

Eventually, STOVs might have useful real-world applications, like their more conventional counterparts. For example, OAM vortices have been used in the design of more powerful stimulated emission depletion (STED) microscopes. STED microscopes are capable of much higher resolution than traditional confocal microscopes, in part due to the precise illumination offered by optical vortices.

With the potential to travel with the central beam at the speed of light, STOVs could have as-yet unforeseen advantages in technological applications, including the potential to expand the effective bandwidth of fiber-optic communication lines.

"A STOV is not just a spectator to the laser beam, like an angel's halo," explained Milchberg, noting the ability of STOVs to control the central beam's shape and energy flow. "It is more like an electrified angel's halo, with energy shooting back and forth between the halo and the angel's head. We're all very excited to see where this discovery will take us in the future."

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In addition to Jhajj and Milchberg, coauthors on the study include IREAP Associate Research Scientist Jared Wahlstrand and physics/IREAP graduate students Sina Zahedpour , Ilia Larkin and Eric Rosenthal.

The research paper, "Spatio-temporal optical vortices," Nihal Jhajj, Ilia Larkin, Eric Rosenthal, Sina Zahedpour, Jared Wahlstrand, and Howard Milchberg, appears in the September 9, 2016 issue of the journal Physical Review X.

This work was supported by the Defense Advanced Research Projects Agency(Award No. W911NF1410372), the Air Force Office of Scientific Research (Award No. FA95501310044), the National Science Foundation (Award No. PHY1301948), and the Army Research Office (Award No. W911NF1410372). The content of this article does not necessarily reflect the views of these organizations.

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Writer: Matthew Wright

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Proximity Effect Realized in Topological Kondo Insulator

Superconductivity in the topologically protected surface states of a three-dimensional topological insulator has been predicted to be a promising platform for exploring exotic quantum states such as Majorana fermion excitations. Although previous efforts have focused on the superconducting proximity effect in bilayer structures between a superconductor and a chalcogenide topological insulator, suppressing the conducting bulk contribution and securing high interfacial transparency between a superconductor and a topological insulator have been major experimental bottlenecks to demonstrating induced superconductivity. Researchers from the Center for Nanophysics and Advanced Materials led by Ichiro Takeuchi, in collaboration with Richard Greene and Johnpierre Paglione, have now demonstrated a supercurrent to flow through the surface layer of the topological Kondo insulator material samarium hexaboride (SmB6) via in situ deposition of a superconducting layer on SmB6 thin films. Published in Physical Review X, this study provides a unique insight into the surface state of SmB6, and marks an important stepping stone for pursuing novel quantum phenomena using thin-film topological insulator devices.

Programmable ions set the stage for general-purpose quantum computers

Quantum computers promise speedy solutions to some difficult problems, but building large-scale, general-purpose quantum devices is a problem fraught with technical challenges.

To date, many research groups have created small but functional quantum computers. By combining a handful of atoms, electrons or superconducting junctions, researchers now regularly demonstrate quantum effects and run simple quantum algorithms—small programs dedicated to solving particular problems.

But these laboratory devices are often hard-wired to run one program or limited to fixed patterns of interactions between their quantum constituents. Making a quantum computer that can run arbitrary algorithms requires the right kind of physical system and a suite of programming tools. Atomic ions, confined by fields from nearby electrodes, are among the most promising platforms for meeting these needs.

In a paper published as the cover story in Nature on August 4, researchers working with Christopher Monroe, a Fellow of the Joint Quantum Institute and the Joint Center for Quantum Information and Computer Science (link is external) at the University of Maryland, introduced the first fully programmable and reconfigurable quantum computer module (link is external). The new device, dubbed a module because of its potential to connect with copies of itself, takes advantage of the unique properties offered by trapped ions to run any algorithm on five quantum bits, or qubits—the fundamental unit of information in a quantum computer.

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Trailing the Photons from Neutron Decay

A high-precision measurement of the photons emitted by neutron decays brings researchers closer to a new test of the standard model. The research, with contributions from UMD Researchers including, Research Scientist and UMD lead  Herbert Breuer, Professor Elizabeth Beise, Alumna Kristin Kiriluk and Affiliate Professors Jeff Nico and Pieter Mumm, was highlighted in APS Physics and is published in Physical Review Letters.

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